1. Field of the Invention
The present invention relates to an optical fiber suitably used for transmission of optical signals or optical power or for optical amplification, and to an optical module including the optical fiber.
2. Description of the Related Art
A highly nonlinear optical fiber has a nonlinear optical coefficient higher than that of an optical fiber that is used as an optical transmission line in optical transmission. The highly nonlinear optical fiber is adopted in, for example, an optical switch, an optical amplifier, and a light generator (see T. Okuno et al., IEEE J. Sel. Top. Quant. Electron. Vol. 5 (1999) 1385). It is known that performance of the highly nonlinear optical fiber is limited by the occurrence of stimulated Brillouin scattering (SBS).
In J. Lightwave Techn. Vol. 19 (2001) 1691, J. Hansryd et al. disclose a method for suppressing SBS by forming a temperature gradient in the longitudinal direction of a highly nonlinear optical fiber so that a Brillouin gain spectrum is nonuniform in the longitudinal direction. In this method, high energy consumption for holding the temperature gradient is a problem. Further, U.S. Pat. No. 5,170,457 proposes to suppress SBS by reducing the number of guided acoustic modes in an optical fiber to zero (by adopting an antiguide structure). In this optical fiber, it is impossible to achieve both light propagation in a narrow area and effective suppression of SBS.